This invention relates to an automatic telephone exchange in which the tone generation is at least partly centralised.
According to the invention, there is provided an automatic telephone exchange, which includes a centrally-located tone generation means which generates tones at a plurality of different frequencies, connections from the generation means to the terminal interfaces for all lines served by the exchange, a central control arrangement for the telephone exchange, and processor means associated with each of said interfaces and adapted to respond to signals from the central control arrangement to apply to a line served by that interface any one of the tones needed by that line, the signals thus applied to the interface controlling both the selection of the tone or tones to be used and the cadences with which the selected tone or tones is or are applied to the appropriate line.